They are well-behaved for a cichlid. They do tend to posture and give short chase to fish they don't want around them on occasion, but it's harmless. Mine just laid eggs last week and they were extra aggressive to the tank mates, but the female never once actually bit another fish, she just chased them away from her eggs.
I did try to introduce neons to my tank a couple weeks ago, but I made the mistake of drip acclimating them for 2 hours and then pouring the bucket into the tank rather than net them in. I feed my frozen brine shrimp to them this way, and they thought I was feeding them. They went after the neons non-stop, but my heavy planting allowed the neons to avoid getting eaten.. I had to move them to my 10 gallon as a result. This same tank has a runt guppy (smaller than a neon) that was in the tank since the Angelfish were dime sized, and they never bat an eyelash at him. He swims near them and eats with them all the time. Your results may vary, of course.
Once they are full grown or close to it, you have to be extra careful how you add new fish if they are small. Feed the tank, shut the lights out, net them in. Chances they go after them as food is much lower.